Mechanisms of Tfr1-mediated iron uptake in bone and effects of iron on bone cell bioenergetics

成骨细胞依靠铁元素的微妙平衡来维持正常的分化和功能。虽然铁对于包括DNA复制、增殖和细胞呼吸在内的各种细胞过程是必需的，但高水平的铁会抑制成骨细胞的功能。尽管有这些知识，我们对铁对成骨细胞的影响的基本了解仍然非常有限。迄今为止，尚不清楚铁如何影响成骨细胞的细胞功能，调节细胞功能涉及哪些代谢途径，以及铁是否根据成骨细胞的分化状态具有相同的影响。甚至不知道铁是如何进入成骨细胞的。在这个项目中，我们将破译这些未解决的方面。我们假设转铁蛋白受体1 （Tfr1）是成骨细胞中主要的铁摄取受体。此外，我们的初步数据使我们假设高浓度的铁以牺牲分化为代价促进成骨细胞增殖，从而限制骨形成。这些假设将通过在稳态和激素缺乏条件下研究成骨细胞特异性Tfr1敲除小鼠的骨表型来验证。由于破骨细胞在骨吸收中起主要作用，而Tfr1在体内的作用也尚未得到解决，我们还将对破骨细胞特异性Tfr1敲除小鼠进行表征。为了研究铁是如何被特定的成骨细胞亚群利用的，我们将使用单细胞RNA测序、非靶向代谢组学和体外功能测试来将代谢谱与特定的成骨细胞亚群及其功能（例如增殖、基质生成和基质矿化）联系起来。该项目将揭示Tfr1对骨骼铁摄取的重要性，并将为铁在成骨细胞功能和生物能量学中的作用提供详细的见解。

Osteoblasts rely on a delicate balance of iron for proper differentiation and function. While iron is necessary for various cellular processes including DNA replication, proliferation, and cellular respiration, high levels of iron suppress osteoblast function. Despite this knowledge, our basic understanding on the impact of iron on osteoblasts remains very limited. To date, it is unclear how iron affects cellular functions in osteoblasts, what metabolic pathways are involved in regulating cell function, and if iron has the same impact depending on the differentiation state of the osteoblasts. It is even unknown how iron enters into osteoblasts. In this project, we will decipher these unresolved aspects. We hypothesize that transferrin receptor 1 (Tfr1) is the main iron-uptake receptor in osteoblasts. Moreover, our preliminary data lead us to hypothesize that high concentrations of iron promote osteoblast proliferation at the expense of differentiation, thereby limiting bone formation. These hypotheses will be tested by investigating the bone phenotype of osteoblast-specific Tfr1 knockout mice under homeostatic and hormone-deficiency conditions. As osteoclasts play a major role in bone resorption and the role of Tfr1 has also not been addressed in vivo, we will also characterize osteoclast-specific Tfr1 knock-out mice. To address how iron is utilized by specific osteoblast subsets, we will use single-cell RNA sequencing, untargeted metabolomics, and functional tests in vitro to link metabolic profiles to specific osteoblast subsets and their function (e.g. proliferation vs. matrix production vs. matrix mineralization). This project will unravel the importance of Tfr1 for iron uptake in the skeleton and will provide detailed insights into the role of iron in osteoblast function and bioenergetics.